1. Field of the Disclosure
This disclosure generally relates to an optical semiconductor structure and, more particularly, to a back side illuminated semiconductor structure with a semiconductor capacitor connected to a floating diffusion node.
2. Description of the Related Art
Conventionally, a floating diffusion node of a back side illuminated semiconductor structure should be large enough such that an equivalent capacitance of the floating diffusion node can be used to store charges after a light sensing region of the light sensing device generates the charges.
However, in the back side illuminated semiconductor structure, as the floating diffusion node is also within an illuminated region of incident light and, unlike the front side illuminated semiconductor structure, does not have a shielding structure consisted of the metal layer, the photoelectric effect also occurs in the floating diffusion node due to the incident light such that the identification to light sensing signals is disturbed and the signal-to-noise ratio is degraded.
In order to reduce the influence to the floating diffusion node by the incident light, conventionally a dimension of the floating diffusion node is reduced as much as possible so as to avoid too much incident light to be received by the floating diffusion node. However, if the dimension of the floating diffusion node is reduced, the equivalent capacitance thereof is decreased as well such that the signal-to-noise ratio is degraded.